The present invention relates to an accelerator system for irradiation with ion beams, and particularly to an accelerator system suitable for a medical application.
Recently, what is called the radiotherapy characterized by irradiating the affected part such as the part affected by cancer with the ion beam has come to attract the attention of the people. In the radiotherapy, it is necessary for the dose of the ion beam for irradiating an affected part to be controlled stably over a wide control range and over a long period time, and, in order to meet these requirements, an accelerating system such as one shown in FIG. 5 has been used conventionally.
The accelerator system shown in FIG. 5 is disclosed in the specification of Japanese Patent No. 2596292 and is designed such that an ion beam B generated at a pre-accelerator 1 including an ion source is deflected by receivers 2, 3 to be transmitted to a post-accelerator 4, where the ion beam is accelerated to acquire a necessary magnitude of energy, and is transmitted, by an emitted beam transmission system 5, to various irradiation rooms (or treatment rooms) 6, 7 and 8 for use in treatment.
When, for instance, a proton beam is used as the ion beam, necessary energy is about 250 MeV, while necessary average current is about 10 nA. Therefore, an apparatus comprising an ion source and a linear accelerator, which are arranged linearly as disclosed in the Japanese Patent Laid-Open No. 10-247600, is usually used as a pre-accelerator 1 where the ion beam B is accelerated to about 10 MeV, while a synchrotron, for instance, is used as the post-accelerator 4.
In this case, for the ion source, a hot-cathode duoplasmatron type ion source or PIG type ion source is used in general, because these ion sources are compact and simple in construction.
Incidentally, the accelerator system according to the prior art shown in FIG. 5 employs a method in which a filter 9 is inserted in an ion beam route on the downstream side of the pre-accelerator to restrict the transmission rate of the ion beam, thereby controlling the ion beam current to be introduced into the treatment rooms 6, 7 and 8.
A metal mesh, a porous plate or the like is used as the filter 9 herein. The metal mesh controls the ion beam level by varying a distance between metal wires and the number of the metal wires, while the porous plate controls the ion beam rate by varying the diameter and the number of apertures.
The above-mentioned prior art has no consideration in that a mount of the ion beam accelerated by the pre-accelerator including the ion source and the linear accelerator is always kept at its maximum throughout the period of irradiation. Thus, problems arise of a low power consumption, the shortening of maintenance intervals, and the prevention of ion beam irradiation with excessive intensity.
More particularly, in the prior art, as explained referring to FIG. 5, a filter 20 is provided in the ion beam route on the downstream side of the pre-accelerator 1 to control the level of the ion beam current. Thus, it is always necessary to keep the ion beam current at its highest level so as to meet the requirement in the treatment room 12 during the irradiation period.
Hence, in the prior art, not only the ion beam current efficiency or the power efficiency is relatively low but also the service life of the equipment becomes relatively short. In consequence, if some faults arise in the filter 20, the beam carrying a large current, without being controlled, will be sent freely to the downstream side. In the prior art, if some faults arise in the filter 20, it is safe for patient by beam current interlock. But it is not good for synchrotron operation.
As a result, the prior art has problems such as not being suitable for the saving of the power consumption, requiring the maintenance at relatively short intervals, and having difficulty in preventing the irradiation with the ion beam of an excessive intensity.
An object of the present invention is to provide an accelerator system having a wide ion beam current control range, suiting a power saving operation, capable of operating at relatively long maintenance intervals and capable of preventing an excessive dose of irradiation from being erroneously transported to the downstream side.
Another object of the present invention is to provide a medical accelerator facility having a wide ion beam control range, suiting a power saving operation, capable of operating at relatively long maintenance intervals and capable of preventing an excessive dose of irradiation from being erroneously transmitted to the downstream side.
In order to attain the above-mentioned objects, the accelerator system is configured to irradiate a target in an irradiation room with an ion beam, which is supplied from a pre-accelerator including an ion source and accelerated by a post-accelerator, and control a value of ion beam current to be applied for the irradiation of the target in the irradiation room by the pre-accelerator.
The above-mentioned objects of the present invention can also be attained by constituting the ion source with at least one of a radio frequency discharge type ion source or a microwave discharge type ion source, or by providing the pre-accelerator with a beam focusing system so that the ion beam current value can be controlled by controlling a focusing rate of the beam focusing system, or by having the pre-accelerator being at least one of a radio frequency linear accelerator or a high-frequency quadrupole accelerator or a drift tube type accelerator so that the ion beam current value can be controlled by controlling at least one of these accelerators or by controlling at least one of the two accelerators provided in combination.
Further, the above-mentioned objects can also be attained by providing the post-accelerator comprising a synchrotron or a cyclotron or a combination of the synchrotron and the cyclotron, or by providing a constitution of enabling the ion beam current value to be controlled according to a predetermined treatment procedure for treatment in the irradiation room, or by using an ion beam being a proton beam.
Further, the above-mentioned objects can also be attained by providing the accelerator system according to any one of the claims 1 through 7 as an accelerator for medical application.